Recently, a pre-crash safety system has been developed in which, a positional coordinate point and a relative velocity of another vehicle relative to an own-vehicle are acquired by a radar device, and a degree of risk of a collision between the other vehicle and the own-vehicle is calculated based on the acquired positional coordinate point and relative velocity, and if it is judged that the degree of risk is high, an appropriate safety measure is taken.
The pre-crash safety system includes: a radar device that acquires the positional coordinate point and relative velocity of the other vehicle; and an electronic control unit (ECU) which calculates, based on the acquired positional coordinate point and relative velocity, the degree of risk of a collision between the other vehicle and the own-vehicle, and which, if it is judged that the degree of risk is high, causes, a seat belt to conduct a fastening operation and a brake to conduct a braking operation.
FIG. 9, FIG. 10, and FIG. 11 are figures showing, in a chronological order, a positional relationship between an own-vehicle 20 equipped with a pre-crash safety system, and another vehicle 21 that is traveling in an oncoming lane. The own-vehicle 20 includes: a radar device 22 that monitors a diagonally forward left direction; a radar device that monitors a forward direction (not diagrammatically represented); and a radar device that monitors a diagonally forward right direction (not diagrammatically represented). 23, which is a reference character, indicates a monitoring area of the radar device that monitors the diagonally forward left direction. As shown in examples in FIG. 9, FIG. 10, and FIG. 11, the monitoring area 23 has a sector-like shape. Diagrammatic representation, of a monitoring area of the radar device that monitors the forward direction and of a monitoring area of the radar device that monitors the diagonally forward right direction, are omitted.
In FIG. 9, FIG. 10, and FIG. 11, a case is being assumed where the other vehicle 21 in the oncoming lane passes by so as to skim a right corner portion of the monitoring area 23, while the own-vehicle 20 is traveling along a leftward-curved road. The radar device 22 acquires a positional coordinate point K of the other vehicle 21 in a constant cycle (e.g. 20 msec). One example of a track of the positional coordinate point K of the other vehicle 21, acquired by the radar device 22 will be described in the following. The track shown in the following is merely one example, and the track of the positional coordinate point K of the other vehicle 21 is not limited to this example.
First, as shown in FIG. 9, a front right corner portion of the other vehicle 21 is acquired as a positional coordinate point K1 of the other vehicle 21. In the next moment, as shown in FIG. 10, a right side portion of the other vehicle 21 is acquired as a positional coordinate point K2 of the other vehicle 21. In the further next moment, as shown in FIG. 11, a rear wheel tire-housing portion of the other vehicle 21 is acquired as a positional coordinate point K3 of the other vehicle 21.
As shown in FIG. 9, FIG. 10, and FIG. 11, in reality, the other vehicle 21 and the own-vehicle 20 are traveling so as to pass by each other. However, as shown in FIG. 11, the positional coordinate point K of the other vehicle 21 is proceeding in a sequence of K1->K2->K3, as if the other vehicle 21 is approaching toward the own-vehicle 20. This is a result of, a point, in which a transmission wave from the radar device 22 is strongly reflected (hereinafter, referred to as a reflection point), moving gradually from the front right corner portion, to the right side portion, and to the rear wheel tire housing portion of the other vehicle 21.
When such a phenomenon occurs, it is difficult for the radar device 22 to determine whether the other vehicle 21 is, in fact, approaching toward the own-vehicle 20, or, due to the movement of the reflection point on the surface of the other vehicle 21, it only appears that the other vehicle 21 is approaching toward the own-vehicle 20. When the radar device falsely recognizes that the other vehicle 21 is approaching toward the own-vehicle 20, even though the other vehicle 21 is, in fact, not approaching toward the own-vehicle 20 (the other vehicle 4 and the own-vehicle 3 are only traveling so as to pass by each other), an incorrect prediction of a collision may be derived if the own-vehicle 3 makes a prediction of a collision based on the positional coordinate point K of the other vehicle 21.
Patent document 1 discloses a technology in which a prediction of a collision is made based on a detection result from a radar device. However, this technology does not consider an occurrence of the phenomenon described above, thus, an incorrect prediction of a collision may be derived when the above described phenomenon occurs.
[Patent Document 1] Japanese Patent Laid-Open No. H6-174846